Plastic materials are recently widely used in manufacturing optical materials, particularly, spectacle lenses because of their light weight, toughness and easiness of dyeing. Optical materials, particularly, spectacle lenses are required to have a low specific gravity, a high transparency, a low yellow degree, a high impact resistance, and optical properties such as a high refractive index and a high Abbe's number.
Polycarbonate known as optical materials having a high impact resistance have some problems of (1) Abbe's number as low as 29, (2) ease of causing optical distortion, and (3) not so high refractive index as low as 1.58, etc.
Japanese Patent Application Laid-Open No. 3-236386 discloses a polythiourethane compound derived from a polythiol compound and an isocyanate group-containing compound. Although higher in the refractive index, the proposed polythiourethane compound is lower than polycarbonates in the impact resistance.
“Latest Polyurethane Applied Technology”, CMC, pp89, 1983 discloses the production of a high-impact material by reacting a polyurethane prepolymer, which is prepared from an OH-terminated polymer and a diisocyanate, with an active hydrogen compound such as amines and polyols. The proposed material is higher in the impact resistance, but lower in the refractive index as compared with polycarbonates.